Heat-action explosive pyrotechnic marker



May 10, 1949. I R. L TUVE HEAT-ACTIONEXPLOSIVE PYROTECHNIC MARKER FiledApril 15, 1944 amen 1M RICHARD L. TUVE atented May 10, 1949 ittAZiHEAT-ACTION EXPLO SIVE' PYROTECHNIC MARK-ER (Granted under the act of'March 3', 1883, as amended April 30, 1928; 370 0. G. 75.7)

5 Claims.

This invention relates to the art of making pyrotechnic devicesand-projectilesof general military utility. Itis particularly concernedwith high explosive projectiles which are characterized by theappearance on bursting of a smoke cloud having a distinguishing color.

In the past various attempts have been made to color thesmoke or cloud.of gases which is formed by a bursting shell, but with no appreciablesuccess. Many attempts to produce colcred bursts have been mad'e'bymixing dyestufis or inorganic pigments'with' the explosive powder or byfilling a core with a dyestufi or pigment and. placing it in the centerof the charge. All of these schemes have proved unsatisfactory becauseno appreciable color was produced if a high explosive charge wasemployed. The methods using inorganic pigments gave no-appreciable coloreven with low explosives. Where colored bursts were obtained; a veryweak explosive charge was used. In such cases theshell became merelyan-inefiective marker;

It is often highly desirable for purposes of accurate aiming in militaryactions to be able to distinguish the hits on .atarget made by shellsfrom difierent guns. This is particularly true when many guns are'hurling shells'into the same general area. The value of shellswhich wouldgive bursts of intensely colored smoke in antiaircraft defense or inthebombardment of shore installations by ship-borne batteries is apparent.

The object of this invention is to provide high explosive shells whichproduce colored bursts of predetermined intense color.

A- second object ofthe invention is'to provide explosive shellscharacterized by the striking color of their bursts and the iact' thattheir explosive power is not substantially less than that of standardhigh explosive shells of the same calibre.

A thirdobject ofth'e invention is to provide novel means for coloringthe bursts of display fireworkssuch as those obtained with largefirecrackers, rockets, and. similar pyrotechnic devices.

A further object of the invention is to provide means for adding'thec'oloring matter, in the form of a coating composition, to=theinterior of the shell.

Other objects of the invention will in part be obvious =and in=partappear hereinafter.

Thisinvention is based onthe discovery that the coloring material inthecloud created by the burst must be in'an" extremely finely divided solidor'liduid' state, such as'smoke or mist, and must be widely dispersedupon bursting of the projectile. In addition the cloud must becomparatively free of other light-absorbing material, particularlycolloidal carbon which appears as a black smoke.

In the practice of this invention a "fine dispersion of the coloringmatter is obtained by employing organic dyestuffs, so placed Within theexplosive shell that, upon bursting of the shell, they are vaporized andthe vapor widely dispersed in the-cloud of explosion products. Contactwith the relatively cold air causes the dyestuffs to condense orsolidify in the form of a fine smoke having an intense color. In orderfor the colored smoke to be clearly visible, an explosive must'b'e usedwhich does not produce adark cloud on detonation. There are a number ofwell-known highexplosives of this type, but two explosives which areespecially good are nitroguanidine and; a mixture comprising ammoniurnpier-ate and ammonium nitrate.

A mixtureof the nitrate and picrate containing from about 40% to aboutammonium nitrate gives excellent performance. When the nitrateis presentin an amount of only 40%, some-carbon is apparent in the burst, as theuncolored cloud is'of agreyish cast instead of white. However; thisslight greyness is not enough to mask the'coloring of the dyestuli toany marked extent. For a perfectly white'burst from the explosivemixture alone stoichiometric proportions of the picrate and nitrate aretheoretically suflicient, according to the following equation:

However, as indicated above, the proportions are not critical. Since thepicrate is easier to handle and preserve in the shell than the nitrate,.it is advantageous-to use less than the stoichiometric amount of thenitrate. I'hese mixtures have approximately the same explosive power asthe picrate alone.

The d'yestufi" may be of any color and composition desired, provided itis solid at ordinary temperatures and that it will vaporize or sublimewithout decomposition on being heated. Dyestufis melting as low as C.are less common than others, but they are perfectly satisfactory.

The'placement of the dyestuii without the shell, in relation to theexplosive, is exceedingly important' because the temperatures reached byhigh explosives ondetonation may exceed three thousand degrees. mixedwith the explosive or it will be dec0mposed in the detonation. At thesame time, hoW-' Thus, the dyestuff cannot be as ever, it must bevaporized and dispersed in the air or cooler gases surrounding the pointof detonation. This is accomplished by placing the dye stuff between theshell casing and the explosive.

The construction of a shell embodying my invention is readily understoodfrom the accompanying simplified drawing in which a casing 53 is showninternally coated with a coloring layer II and filled with explosivecharge i2. cases an inert separator or insulator 13 between charge l2and color coating II is of value but ordinarily it is not necessary.,After coating the inside of the shell casing In as described below theexplosive charge I2 is inserted along with the standard time fuz e orcontact detonator M and the shell casing is closed.

The method of applying the color coating to the inside of the shell canbe worked out according to the convenience of the manufacturer. Rotationof the shell with the molten coloring matter therein and letting itsolidify gradually has been found satisfactory. Likewise mixing thecoloring matter with wax or thermoplastic resin of fairly low meltingpoint such as ordinary paraifln or methyl methacrylate and applying themixture to the inner wall of the shell by rotation of the casingcontaining the fluid mixture is quite satisfactory. A solution of thewax or resin and dye in a volatile solvent applied as outlined alsogives satisfactory results. familiar to any chemist and it isunnecessary to describe them in any greater detail,

It has been found that a solution of an organic hinder or resin likemethyl methacrylate in toluene with the dyestufi as pigment forms a verysatisfactory paint for coating the inner surface of the shell. Forexample a solution of about 20% methyl methacrylate in toluene acting asVehicle for the dyestufi forms a paint which forms a good adherentcoating for the inside of the shell. This method of applying the coloris an effective substitute for melting the dyestuif itself in the shellcasing.

Although many different satisfactory dyestufi's can be found by testingthem for evaporation or sublimation by dropping them in the form ofpowder on a hot plate, the following dyestuffs are typical of thosewhich have been tested and found to give excellent results: for a red ororange smoke, xylene azo beta naphthol, benzene azo beta naphthol,diethyl m-amino phenolphthalein hydrochloride; for a yellow smoke, aminoazo toluene and benzene azo dimethylaniline; for a blue smoke,quinazarin blue, alizarine cyanine green, anthraquinone violet. Thislist could be expanded greatly by means of the simple preliminary testindicated above. Likewise the colors of bursts can be varied by usingmixtures of the dyes but since sharp diiferences in colors of bursts aregenerally desired it is not expected that great attention will be paidto shading of the bursts.

Many test projectiles of the 3 inch and 5 inch anti-aircraft type weremade and fired, at both high and low elevation and against various kindsof backgrounds. All bursts were in sunlight. The bursts for the 3 inchshells were set for 5 seconds after firing, and the 5 inch shells wereset for 15 seconds. At these distances all the colors weredistinguishable but the yellows and greens faded rapidly. The red-orangebursts were relatively permanent and were diluted to a pink only afterabout three minutes. The 5 inch shell bursts were particularly striking.Generally, about of the total charge in the shell was dyestuif, whichwas put in place either by melting and coating These techniques arequite In some the shell sides as described or coating the shells with asolution of a binder in which the dye was dispersed. These testsrevealed the following facts:

1. It is important, for maximum color, that the greater part of thedyestuif be placed on the sides of the shell and not on the bottom.

2. Increasing the proportion of dye used while keeping the coated areaconstant, results in an I increase in volume of the color cloud.

3. The use of a thick paint comprising an organic resinous binder and avolatile solvent as vehicle for the dye for coating the inside of theshell results in an effective substitute for the melting of the dyestuffitself in the shell casing.

4. Those dyestuffs which have a low melting point and high volatilitygive the greatest volume of color cloud per unit weight of dyestuffused.

5. The temperatures reached in the detonation do not adversely effecteven the most readily oxidizable dyestuffs when they are coated on theinner wall of the shell casing.

Since certain changes can be made in the projectile or pyrotechnicdevice described and different embodiments of the invention could bemade without departing from the scope of this invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawing shall be interpreted as illustrative and not in alimiting sense.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon 01' therefor.

Iclaim:

l. A pyrotechnic device comprising a hollow casing, an explosive chargewithin the casing and a normally solid, vaporizable azo dye having amelting point not over 0., said dye being volatilizable at the explosiontemperatures of the charge and condensible in colored aggregates atatmospheric temperatures, said dye being positioned between theexplosive charge and the casing and applied as a coating to the insidewall of the casing.

2. An explosive marker shell comprising a hollow casing, a sheet of azodye covering and adhering to the inside Wall of the casing, said dyebeing vaporizable and condensible in the atmosphere without substantialdegradation and having a melting point below 150 0., the dye sheetoperative on detonation of the explosive and rupture of the casing tovaporize and disseminate for atmospheric condensation in coloredaggregates.

3. An explosive marker shell characterized by its ability to produce acolored burst of smoke which comprises a hollow casing, a charge ofexplosive within said casing and a normally solid coating of an azo dyehaving a melting point not over 150 C. adhering to the inside wall ofthe casing, said dye being volatilizable at the explosion temperaturesof the charge and condensible in colored aggregates at atmospherictemperatures, said explosive charge being a, mixture of about 40% toabout 75% ammonium nitrate and the balance ammonium picrate.

4. An explosive marker shell characterized by its ability to produce acolored burst of smoke which comprises a hollow casing, a charge ofexplosive within said casing and a normally solid coating of an azo dyehaving a melting point not over 150 C. adhering to the inside wall ofthe casing, said coating bonded by a methyl methacrylate resin, said dyebeing volatilizable at the explosion temperatures of the charge andcondensible in colored aggregates at atmospheric temperatures and saidexplosive charge being a mixture of about 40% to about 75% ammoniumnitrate and the balance ammonium picrate.

5. An explosive marker shell characterized by its abilit to produce acolored burst of smoke which comprises a hollow casing, a charge ofexplosive within said casing and a normally solid coating of an azo dyehaving a melting point not over 150 C. adhering to the inside wall ofthe casing, said coating bonded by a paraffin, said dye beingvolatilizable at the explosion temperatures of the charge andcondensible in colored aggregates at atmospheric temperatures and saidexplosive charge being a mixture of about 40% to about 75% ammoniumnitrate and the balance ammonium picrate.

RICHARD L. TUVE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 262,440 Linton Aug. 8, 1882675,472 Ford June 4, 1901 1,428,011 Dahn Sept. 5, 1922 1,451,395Hustvedt et a1 Apr. 10, 1923 2,108,019 Neukirch Feb. 8, 1938 FOREIGNPATENTS Number Country Date 17,788 Great Britain (1908)- Feb. 11, 1909126,740 Great Britain May 22, 1919 128,986 Great Britain July 10, 1919745,599 France Feb. 21, 1933

